1. Field of the Invention
The present invention relates to a variable valve mechanism for an internal combustion engine which varies a phase of an intake valve or exhaust valve.
2. Description of the Related Art
From the viewpoint of suppression of exhaust gas from an engine, many variable valve mechanisms for an engine mounted in a vehicle are configured to adjust opening and closing times of inlet and exhaust valves or to adjust the opening period of these valves.
As an example of the constitution of the variable valve mechanism, for example, there is proposed a constitution to transmit the displacement of a cam lift of a cam, which is provided in a camshaft, to a reciprocating swing cam, in which a base circular section and a lift section are continuous to each other, by using a center rocker arm as a transmission member, and thereby to drive an inlet valve and an exhaust valve by a rocker arm driven by the swing cam.
The posture of the center rocker arm is adjusted by, for example, an actuator. When the posture of the center rocker arm is changed, a position contacting with a cam is changed in the center rocker arm, and at the same time, a position contacting with the swing cam is changed in the center rocker arm. As a result, the operations in the inlet valve and the exhaust valve are changed.
As mentioned above, the cam and the center rocker arm come into contact with each other, and at the same time, the center rocker arm and the swing cam come into contact with each other, whereby the swing cam and the rocker arm come into contact with each other.
Specifically, a roll-like cam follower is provided in the center rocker arm. The cam follower is in rolling contact with the cam. A surface coming into slidable contact with the front end surface of the center rocker arm is formed in the swing cam. The rocker arm is provided with a roller member. The swing cam is in rolling contact with the roller member. Such a technique is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-299536.
As mentioned above, the variable valve mechanism is provided with a plurality of components, that is, the center rocker arm, the swing cam, and the rocker arm. When the adjacent components of these components (e.g., combination of the cam and the center rocker arm, combination of the center rocker arm and the swing cam, and the combination of the swing cam and the rocker arm) come into contact with each other, and at the same time, slid with each other, it is preferable to provide, in the contact part, an inner ring, an outer ring, and a rolling roller member in which a rolling element is accommodated between the inner ring and the outer ring as with a needle roller member for the purpose of suppressing friction generated at the contact part.
Meanwhile, in the constitution in which the displacement of the cam is transmitted in the order of the center rocker arm, the swing cam, and the rocker arm, as the constitution of the variable valve mechanism disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-299536, the load generated in transmitting the displacement of the cam to the components positioned between the valves, that is, the center rocker arm, the swing cam, and the rocker arm acts on the contact part between the cam and center rocker arm and the contact part between the center rocker arm and the swing cam which are far from the valve driven by the variable valve mechanism in a transmission path through which the displacement of the cam is transmitted.
Specifically, the load, which can transmit the displacement of the cam to the valve through the center rocker arm, the swing cam, and the rocker arm, acts on the contact part between the cam and the center rocker arm. Meanwhile, the load, which can transmit the displacement of the cam to a surface through the swing cam and the rocker arm, acts on the contact part between the center rocker arm and the swing cam.
As a result, it is considered that the deformation such as deflection occurs in the contact part between the cam and the center rocker arm and in the contact part between the center rocker arm and the swing cam, thereby generating a loss in the displacement of the cam to be transmitted to the valve driven by the variable valve mechanism. It is unpreferable to generate the loss of the displacement of the cam to be transmitted.
However, the needle roller member having the above constitution is easily deformed with respect to the load acting from the outer ring toward the inner ring. This point will be described in detail as follows. The needle roller member has a plurality of needles accommodated between the outer ring and the inner ring.
When the load acts from the outer ring toward the inner ring, the load is transmitted from the outer ring to the needles. At this time, if the load acts on a gap between the adjacent needles, it is considered that the outer ring is deformed so as to correspond to the gap.
Therefore, if the needle roller member is used in consideration of the friction, it is considered that the loss in the transmission of the displacement of the cam is due to the deformation of the needle roller member.
Meanwhile, in this type of variable valve mechanism described above, the swing cam is provided with a pin member for receiving the displacement of the center rocker arm. Specifically, a groove is provided in the pin member. The groove has a bottom surface, which comes into slidable contact with a front end surface of the center rocker arm in response to the displacement in the posture and position of the center rocker arm while transmitting the displacement of the cam. The front end part of the center rocker arm is accommodated in the groove of the pin member in a slidable manner.
The center rocker arm is then supported by, for example, a rocker shaft for supporting the rocker arm in a swingable manner. The posture of the rocker shaft is adjusted by, for example, an actuator. When the posture of the rocker shaft is changed, the position of a part supported by the rocker shaft is also changed in the center rocker arm. The posture of the center rocker arm is also changed following that change.
When the posture of the center rocker arm is changed, the position contacting with the cam is also changed in the center rocker arm, and at the same time, the position contacting with the swing cam is also changed in the center rocker arm. Thereby, the operation in the inlet and exhaust valves is changed. This kind of technique is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-299536.
As mentioned above, in the variable valve mechanism disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-299536, the cam and the center rocker arm come into contact with each other, the center rocker arm and the swing cam come into contact with each other, and the swing cam and the rocker arm come into contact with each other. Particularly, the center rocker arm and the swing cam come into slidable contact with each other, and thus the contact part between them needs to be lubricated with lubricating oil.
However, as in Jpn. Pat. Appln. KOKAI Publication No. 2005-299536, when the center rocker arm and the swing cam come into slidable contact with each other, the contact area between them becomes relatively larger. Thus, a relatively large amount of lubricating oil is required.
Meanwhile, it is considered that the adjacent components come into line contact with each other by providing a roller member in the contact part between the adjacent components along a transmission path through which the displacement of the cam is transmitted to the valve. The constitution in which the adjacent components come into line contact with each other can reduce the amount of lubricating oil.
Further, it is considered that the lubricating oil is dispersed by the rotation of the roller member. This dispersion of the lubricating oil can realize the lubrication of the components around the contact part such as a support part of the rotation shaft of the roller member.
Meanwhile, the variable valve mechanism disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-299536 has the constitution in which the front end surface of the center rocker arm comes into slidable contact with the groove of the pin member provided in the swing cam, whereby the center rocker arm is fitted into the groove to thereby position the center rocker arm.
However, in the constitution using the roller member in the contact part between the center rocker arm and the swing cam, when the center rocker arm is displaced in a different direction from a predetermined displacement direction, it is considered that the center rocker arm assumes a different posture from a predetermined posture.
In this manner, the posture of the center rocker arm with respect to the swing cam and the cam is changed. Specifically, the posture of the front end surface of the center rocker arm with respect to the roller member of the swing cam is changed. If the posture of the front end surface of the center rocker arm with respect to the roller member is changed, the displacement of the cam transmitted to the swing cam through the center rocker arm has an error in the initially determined transmission of the displacement of the cam.
It is considered that such an error causes an error in the displacement of the cam, being transmitted to the valve driven by the variable valve mechanism, against the initially determined displacement of the cam. Thus, it is unpreferable that the center rocker arm being driven assumes a different posture from the predetermined posture.